It is often desirable to have a uniform light source. For example, in a backlit panel display, such as in advertising or in a display screen, a backlight advantageously illuminates the display surface. Such backlights are preferably uniform and bright and occupy a minimum of space.
Generally two approaches are used to provide such illumination. In one approach, a single light source is positioned behind the display, often using a central light emitter and a reflective dish. One such illuminator is described by Ogawa et al. in U.S. Pat. No. 4,803,399. Such systems have limited applicability in flat panel types of displays, in part, because they require a relatively large volume to spread the light and have nonuniformities caused by the cathodes being exposed.
One approach to lighting which can reduce this problem is the use of a flat panel fluorescent lamp. Such lamps can provide a wide area of relatively uniform illumination while occupying a relatively small volume. However, such planar fluorescent lamps are often difficult and expensive to fabricate in large sizes. Even if such larger lamps were readily producible, such large, flat fluorescent displays are typically fragile. Moreover, uniformity of light distribution is hard to produce and maintain in large lamps.
To reduce the problems associated with large flat panel fluorescent lamps, multiple lamps may be tiled in a two-dimensional array. In such an array the light sources may be positioned substantially adjacent each other, overcoming in large part, the dead space between light sources of the multiple lamp approach discussed above.
Even where lamps are tiled, uniformity problems may exist. In conventional flat planar fluorescent lamps, a region of little or no illumination typically surrounds the electrodes used to generate a discharge current. Such dark regions, known as Crooke's spaces and Faraday dark spaces, detract from the uniformity of the display, causing "dark" regions in the lamp.
Tiling of lamps does not eliminate the non-uniformity caused by the dark regions. In a tiled array of conventional planar fluorescent lamps, the dark regions remain, causing the light to be non-uniform. Even when lamps are not for use in large panel applications, such dark regions are undesirable. For instance, when lamps are used in heads-up displays in aircraft or as backlights to smaller displays, such dark regions can cause undesirable variations in an illuminated image.